The former Warriors skipper's positional switch prompted theories about whether Auckland had fielded any phone calls from an All Blacks coaching staff that had found little time for Tuivasa-Sheck in midfield.
But McGrath, who after the Taranaki win denied any intervention from above, insisted it was an internal decision and one that reaped the desired results.
"We were rapt with what Roger did last week," he said. "It was a wet, miserable day and you want your winger to chase kicks, you want your winger to catch high balls. He did that in spades, so we're happy with him there and I think we just want to let him develop out there.
"Changing him back to 12 at this stage after playing last week on the wing probably wasn't the right thing to do for Roger or for the team."
Tuivasa-Sheck's agency in his playing role has been largely overlooked but, trailing in the All Blacks' midfield queue, his ability to play well on the wing will only boost his prospects of securing a trip to next year's World Cup.
Yet McGrath said that also was of little concern to the Auckland coaches, whose focus was on picking a team to beat Taranaki and now North Harbour.
"We wanted Roger to roam about and get his hands on the ball as much as he could. Obviously the day wasn't like that because of the weather, but he did everything that we asked of him.
"So it wasn't a case of trying to get him into All Blacks selection because he can play different positions – it was about we had some good midfielders and we just wanted Roger to relax and enjoy his footy."
Joining Tuivasa-Sheck in that aim tomorrow will be fellow All Blacks Akira Ioane, Angus Ta'avao and Patrick Tuipulotu, with the lock returning from injury and providing an invaluable boost as Auckland continue their quest to win their first title since 2018.
"We're grateful to have them back, but we know that just having them back is not going to get the job done. We have to do this as a 23," McGrath said. "We've spoken all week about every individual doing their job and not relying on others to get us over the line. So it's all about a collective group."
Auckland
Jordan Trainor, Roger Tuivasa-Sheck, AJ Lam, Corey Evans, Tomas Aoake, Harry Plummer, Taufa Funaki, Jackson Pugh, Blake Gibson, Akira Ioane, Hamish Dalzell, Patrick Tuipulotu, Angus Ta'avao, Soane Vikena, Alex Hodgman.
Reserves: Leni Apisai, Jordan Lay, Marcel Renata, Josh Beehre, Terrell Peita, Manu Paea, Simon Hickey, Jock McKenzie.
North Harbour
Shaun Stevenson, Mark Telea, Moses Leo, Henry Taefu, Tevita Li, Bryn Gatland, Jamie Booth, Cameron Suafoa, Jed Melvin, Tamarau McGahan, Felix Kalapu, Isoa Nasilasila, Nic Mayhew, Ray Niuia, Tevita Langi.
Reserves: Luteru Tolai, Alex Fidow, Sam Davies, Danny Drake, Lotu Inisi, Siaosi Nginingini, Fine Inisi, Kade Banks.